Electrical cables customarily comprise one or more conductors surrounded by an insulating medium, and a protective sheath. Such cables are used for the transmittinq of electrical power and in the transmission of communications signals. Power cables have relatively few conductors of heavy gauge which are insulated for high voltages. Communications cables usually contain many pairs of small gauge, paper insulated copper conductors, surrounded by an external lead or plastic sheath. The various pairs of conductors are arranged by twisting and placement to minimize pick-up, i.e., cross talk, between them.
In recent years, wide use has been made of underground cables for the transmission both electrical power and communications. Aside from the obvious aesthetic advantages provided by underground power distribution and communications networks, such underground placement of cables offers relative immunity from damage due to environmental factors such as lightening, high winds and ice formation.
One of the problems realized in maintaining the many miles of underground cable which have been laid over the years is that of water intrusion, corrosion and galvanic action which takes place due to the presence of dissimilar metals in the cables. These actions produce undesirable electrical shorting of the cable pairs in the cable core and cause noise, interference and cross-telephone conversations in the telephone lines which are served by the cable.
Various techniques have been proposed to alleviate problems caused by water intrusion including pumping of liquids and gases, such as air and nitrogen through the cables to clear the cable of water and dry the telephone cable pairs.
Various types of compounds such as copper sulfate and sulfuric acid are formed in the cables over time. Subsequent water intrusion reacts with these compounds and results in changes the capacitance of the cable, which increases the noise level in telephone conversations. This problem is further complicated by the fact that many core cables include an outer plastic sheath, an intermediate liner constructed of a metal such as copper, aluminum or steel metal and optional plastic liners, which contains the cable pairs. Under circumstances wherein the inner plastic sheath is worn, pitted or otherwise damaged thus facilitating water intrusion into the metal jacket, or wherein no plastic inner sheath is placed in the cable, the copper, aluminum or steel oxidizes and forms compounds which are detrimental to the life and service of the cable pairs located in the cable.
A number of methods have been proposed to protect or restore underground cables which have been damaged due to water intrusion. Bahder, U.S. Pat. No. 4,372,988 and Vincent et al, U.S. Pat. No. 4,766,011 teach similar methods of protecting underground cables which involve supplying the cables with solutions which basically fill-in and seal voids in the cable where water might leak into the cable.
Vincent et al, U.S. Pat. No. 3,252,834 discloses a preservative treatment for electrical cables wherein a liquid mixture of varnish, silicone resin and a suitable solvent are pumped through a section of an underground so that the varnish coats the interior of the cable and conductor insulation.
A more recent underground cable treatment method is disclosed by Senn in U.S. Pat. No. 4,783,226. This patent discloses an apparatus which is used to sequentially pump air and treating liquid through a sealed off portion of the cable. The treating liquids used in this patent include low viscosity, light demoisturizing insulating and cleaning oils which were specifically selected to clean and restore plastic insulated cables.
It has subsequently been discovered that the prior art cable cleaning and restoration liquids are suitable for use in conjunction with plastic insulated cable, but are unsuited for use in conjunction with paper insulated cable. A major disadvantage discovered which makes the prior art cleaning and restoration formulation unacceptable for use in conjunction with paper insulated cables is that the low viscosity components conventionally used include hydrocarbon oils which leave residues on the paper insulation which render the insulation too conductive for proper use.
The cleaning and restoration formulations of the present invention are a substantial improvement over the prior art which allow for cleaning and restoration of paper insulated cables without imparting appreciable conductivity to the paper insulation.